When encountering duplicated item names, register error resolution to avoid further errors

As one example from our test suite, the following test has a duplicated name error, where the latter resolution is registered, which causes any use of the item when expecting the first causes subsequent errors:

https://github.com/rust-lang/rust/blob/fffc4fcf96b30bc838551de5104d74f82400b35b/tests/ui/traits/issue-106072.stderr#L1-L23

Ideally when encountering duplicated names we should register that name as an error Res so that subsequent uses do not emit any errors. Fixing the duplicated names might cause subsequent errors to happen from any case where we were expecting the latter item, but it's just a coin toss in the end (and when adding a new item shadowing an existing one, the existing one is likely to have many more usages than the new one). Doing this trades less verbosity when encountering this for at least one additional compile cycle to get the errors of incorrect uses. An alternative would be to collect all access to duplicated items and emit a single error for them, but that might need additional complicated Resolver logic.

Start with tests/ui/traits/issue-106072.stderr and trace the compiler resolver's handling of duplicated names and the Resolver logic mentioned in the issue. Confirm the current diagnostics and identify the relevant duplicate-name resolution path. Done means duplicated names register an error Res so later uses do not produce follow-on errors, with UI expectations updated accordingly.